Metal cutting inserts having a variety of chip controlling shapes are known in the art. U.S. Pat. No. 3,654,681 discloses a metal cutoff tool characterized by the fact that the cutting portion thereof is provided with a chip breaker surface that includes opposed chamfer surfaces located rearwardly of the cutting edge that assist in providing clearance for chip removal purposes. U.S. Pat. No. 3,815,191 teaches a chip forming insert that imparts a longitudinally extending bulge to a chip which stiffens the chip and modifies its form. U.S. Pat. No. 3,973,308 teaches a cutting tool that has several depressions or notches separated from each other and situated inside and spaced from the cutting edge. U.S. Pat. No. 4,629,372 to Huston discloses a cutting insert having a chip breaking surface that is intended to be used as a parting or cutoff tool. Known cutting insert designs, when used on low strength, ductile steels inherently experience several problems. Examples of low strength, ductile steels include 304L and 316L stainless steel, as well as 1010 and 1026 carbon steel with reduced strength for easier drawing over a mandrel to form tubing.
The task of controlling chips during a cutoff operation is made more difficult when a lead angle is employed to ensure that the manufactured part is cleanly severed from the tube and bar stock. Chips formed by a lead angle cutoff tool tend to flow in a direction normal to the cutting edge. This will cause the cutoff chip generated on initial contact with the workpiece to flow more readily into a spiral shape because of the force component in the axial direction, rather than the more desirable clock spring shape which is more readily controlled. A number of techniques have been used to offset the tendency of the cutoff chip to be directed primarily by the lead angle so that a spiraling chip is formed. Techniques have included a chip breaker which was unbalanced about the centerline of the tool, such that it opposed a spiraling tendency. Another technique tried is providing a chip breaker whose back wall was of equal magnitude but in an opposite direction to the lead angle. Still another technique tried is the use of a non-uniform height cutting edge which opposes the effect of the lead angle by attempting to introduce a counter force to the lead angle's axial force. While these techniques were sufficient on some jobs, they tended to be very limited in range and frequently increased cutting pressure to obtain chip control, sacrificing tool life in the process.
Cutting inserts such as those described above are typically held in a tool holder forming part of a cutting tool assembly. The tool holder is typically part of a slide mechanism which presents the insert in a predetermined operative position determined by the operation to be performed. It should be apparent that high forces are exerted on the cutting insert and the tool holder when performing machining operations such as grooving, severing or profiling. A given cutting tool assembly is generally used with various cutting inserts including inserts having a cutting edge oriented at a lead angle, as well as inserts having a cutting edge oriented square with respect to the longitudinal axis of the insert.
Integral shank tool holders utilizing a flexible upper section which is hinged in such a fashion that a fastener, when tightened, deflects the section such that it rigidly clamps a double ended, V-bottom insert are well known in the art. Besides having the benefit of a one piece, rigid structure that ensures the orthogonal presentation of the cutting insert to the workpiece, the tool holder also simplifies inventory, ordering and programming functions by serving as a standard platform for a variety of insert configurations. It is desirable to have V-bottom grooving inserts of a particular width, but of varying corner radii, V-bottom profiling inserts, as well as cutoff inserts to be accommodated by the same holder, allowing multiple combinations of functions to be performed with a common tool holder. Of importance to ensuring consistent performance of all these cutting tool inserts it the ability to support the insert against tangential and radial cutting forces both below and behind the insert. The V-bottom supporting configuration ensures this common, rigid support underneath the cutting insert. The tool holder typically is designed with an accurately machined locating surface against which the unused edge of the double ended insert is positioned. This locating surface performs at least two functions, i.e., that of insuring resistance to cutting forces in the radial direction and also of accurately positioning the insert radially in order to insure proper groove depths or complete cutoff. The locating surface of the tool holder is generally planar and is positioned at such an angle as to exactly match the mating, planar clearance surface of the front of the cutting insert which will be positioned against it. This surface is located so that it is parallel to the axial centerline of the workpiece.
Some cutoff inserts utilize a lead angle for insuring a part is completely severed without leaving an undesirable nib or pip on the part. When this type of insert is mounted in the type of tool holder described above, the planar tool holder backup locating surface which securely supports grooving or straight cutoff inserts will no longer be able to offer a large contact area, but much weaker and less dimensionally consistent line contact. Several techniques to address this issue are known in the art. These techniques have not been totally satisfactory and, in some cases, added unwanted expense to the cost of manufacturing the insert.